Rigidity controls human desmoplastic matrix anisotropy to enable pancreatic cancer cell spread via extracellular signal-regulated kinase 2

Abstract

It is predicted that pancreatic ductal adenocarcinoma (PDAC) will become the second most lethal cancer in the US by 2030. PDAC includes a fibrous-like stroma, desmoplasia, encompassing most of the tumor mass, which is produced by cancer-associated fibroblasts (CAFs) and includes their cell-derived extracellular matrices (CDMs). Since elimination of desmoplasia has proven detrimental to patients, CDM reprogramming, as opposed to stromal ablation, is therapeutically desirable. Hence, efforts are being made to harness desmoplasia's anti-tumor functions. We conducted biomechanical manipulations, using variations of pathological and physiological substrates in vitro, to culture patient-harvested CAFs and generate CDMs that restrict PDAC growth and spread. We posited that extrinsic modulation of the environment, via substrate rigidity, influences CAF's cell-intrinsic forces affecting CDM production. Substrates used were polyacrylamide gels of physiological (~1.5 kPa) or pathological (~7 kPa) stiffnesses. Results showed that physiological substrates influenced CAFs to generate CDMs similar to normal/control fibroblasts. We found CDMs to be softer than the corresponding underlying substrates, and CDM fiber anisotropy (i.e., alignment) to be biphasic and informed via substrate-imparted morphological CAF aspect ratios. The biphasic nature of CDM fiber anisotropy was mathematically modeled and proposed a correlation between CAF aspect ratios and CDM alignment; regulated by extrinsic and intrinsic forces to conserve minimal free energy. Biomechanical manipulation of CDMs, generated on physiologically soft substrates, leads to reduction in nuclear translocation of pERK1/2 in KRAS mutated pancreatic cells. ERK2 was found essential for CDM-regulated tumor cell spread. In vitro findings correlated with in vivo observations; nuclear pERK1/2 is significantly high in human PDAC samples. The study suggests that altering underlying substrates enable CAFs to remodel CDMs and restrict pancreatic cancer cell spread in an ERK2 dependent manner.

Keywords: Cancer associated fibroblasts; Cell-derived extracellular matrix; Desmoplasia; Fiber alignment; Matrix-induced responses; Pancreatic cancer; Underlying substrate stiffness.